scholarly journals DYNAMIC FIELD DATA FROM OFFSHORE MONOPILE WIND TURBINES – ASSESSMENT OF NATURAL FREQUENCIES AND DAMPING

2020 ◽  
Author(s):  
Karin Norén-Cosgriff ◽  
Amir M. Kaynia
Keyword(s):  
Wind Turbines ◽  
Field Data ◽  
Natural Frequencies ◽  
Dynamic Field

scholarly journals Comparative Modal Analysis of Monopile and Jacket Supported Offshore Wind Turbines including Soil-Structure Interaction

2020 ◽  
Vol 20 (10) ◽  
pp. 2042016
Author(s):  
A. Abdullahi ◽  
Y. Wang ◽  
S. Bhattacharya
Keyword(s):  
Wind Turbines ◽  
Soil Structure ◽  
Natural Frequencies ◽  
Model Updating ◽  
Offshore Wind ◽  
Fe Model ◽  
Analysis And Design ◽  
Offshore Wind Turbines ◽  
Future Design ◽  
Wide Range

Offshore wind turbines (OWTs) have emerged as a reliable source of renewable energy, witnessing massive deployment across the world. While there is a wide range of support foundations for these structures, the monopile and jacket are most utilized so far; their deployment is largely informed by water depths and turbine ratings. However, the recommended water depth ranges are often violated, leading to cross-deployment of the two foundation types. This study first investigates the dynamic implication of this practice to incorporate the findings into future analysis and design of these structures. Detailed finite element (FE) models of Monopile and Jacket supported OWTs are developed in the commercial software, ANSYS. Nonlinear soil springs are used to simulate the soil-structure interactions (SSI) and the group effects of the jacket piles are considered by using the relevant modification factors. Modal analyzes of the fixed and flexible-base cases are carried out, and natural frequencies are chosen as the comparison parameters throughout the study. Second, this study constructs a few-parameters SSI model for the two FE models developed above, which aims to use fewer variables in the FE model updating process without compromising its simulation quality. Maximum lateral soil resistance and soil depths are related using polynomial equations, this replaces the standard nonlinear soil spring model. The numerical results show that for the same turbine rating and total height, jacket supported OWTs generally have higher first-order natural frequencies than the monopile supported OWTs, while the reverse is true for the second-order vibration modes, for both fixed and flexible foundations. This contributes to future design considerations of OWTs. On the other hand, with only two parameters, the proposed SSI model has achieved the same accuracy as that using the standard model with seven parameters. It has the potential to become a new SSI model, especially for the identification of soil properties through the model updating process.

scholarly journals Tripod-Supported Offshore Wind Turbines: Modal and Coupled Analysis and a Parametric Study Using X-SEA and FAST

2019 ◽  
Vol 7 (6) ◽  
pp. 181 ◽  
Author(s):  
Pasin Plodpradit ◽  
Van Nguyen Dinh ◽  
Ki-Du Kim
Keyword(s):  
Wind Turbines ◽  
Natural Frequencies ◽  
Offshore Wind ◽  
Computational Time ◽  
Coupled Analysis ◽  
Physical Interaction ◽  
Support Structures ◽  
Coupled Models ◽  
Support Structure ◽  
Offshore Wind Turbines

This paper presents theoretical aspects and an extensive numerical study of the coupled analysis of tripod support structures for offshore wind turbines (OWTs) by using X-SEA and FAST v8 programs. In a number of site conditions such as extreme and longer period waves, fast installation, and lighter foundations, tripod structures are more advantageous than monopile and jacket structures. In the implemented dynamic coupled analysis, the sub-structural module in FAST was replaced by the X-SEA offshore substructure analysis component. The time-histories of the reaction forces and the turbine loads were then calculated. The results obtained from X-SEA and from FAST were in good agreement. The pile-soil-structure interaction (PSSI) was included for reliable evaluation of OWT structural systems. The superelement concept was introduced to reduce the computational time. Modal, coupled and uncoupled analyses of the NREL 5MW OWT-tripod support structure including PSSI were carried out and the discussions on the natural frequencies, mode shapes and resulted displacements are presented. Compared to the uncoupled models, the physical interaction between the tower and the support structure in the coupled models resulted in smaller responses. Compared to the fixed support structures, i.e., when PSSI is not included, the piled-support structure has lower natural frequencies and larger responses attributed to its actual flexibility. The models using pile superelements are computationally efficient and give results that are identical to the common finite element models.

Atmospheric Ice Loading and its Impact on Natural Frequencies of Wind Turbines

2015 ◽  
Vol 39 (1) ◽  
pp. 83-96 ◽  
Author(s):  
Abdel Salam Y. Alsabagh ◽  
Yigeng Xu ◽  
Muhammad S. Virk ◽  
Omar Badran
Keyword(s):  
Wind Turbines ◽  
Natural Frequencies

Research Modal Analysis Method of MW Wind Turbines

2013 ◽  
Vol 423-426 ◽  
pp. 1524-1530
Author(s):  
Yong Shui Luo ◽  
Min Qiang Zhou ◽  
Wei Jiang Liu ◽  
Qi Chen ◽  
Shou Bin Wang
Keyword(s):  
Boundary Conditions ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Natural Frequencies ◽  
Theoretical Data ◽  
Rotor System ◽  
Resonance Phenomenon ◽  
Cross Point ◽  
Operation Speed ◽  
The Cross

In order to explore the modal characteristics of the wind turbine, this paper researches how these natural frequencies of the major structural components within the operation speed range to avoid coupled resonance phenomenon. Aiming at 1500kW variable speed variable pitch double-fed wind turbines which are the mature products in market, the whole wind turbine dynamic modal equations are established by Lagrange method, and then process on-site testing is carried out to obtain measured modal characteristic parameters. The results of both theoretical and measured dates show that deviation between theoretical data and measured data, how the subsystem boundary conditions simplified methods to influence the rotor system natural frequencies, how the subsystem boundary conditions simplified methods to change the cross point of the rotor system natural frequencies with rotor speed 3P, and solution for wind turbine pass the cross point. The results will provide a certain extent guidance for the wind turbine development, design and optimization.

Comparison of Three Different TLPs for Wind Turbines by Tank Tests and Calculated Results

2015 ◽  
Author(s):  
F. Adam ◽  
T. Myland ◽  
F. Dahlhaus ◽  
J. Großmann
Keyword(s):  
Wind Turbine ◽  
Dynamic Behavior ◽  
Wind Turbines ◽  
Main Part ◽  
Natural Frequencies ◽  
Type Structure ◽  
Offshore Wind ◽  
Wave Loads ◽  
Offshore Wind Turbines ◽  
Short Overview

This paper will give a short overview of the path of development of the so called GICON® - Tension Leg Platform (TLP) for offshore wind turbines. The main part of the paper will provide a summary as well as insights from three different model basin tests. Furthermore, the comparison of a truss like structure (first concept) with a shell type structure (third concept) deduced from the measured results and also by comparison of the natural frequencies will be presented. Both structures were tested in wave tanks in a scale of 1:25. The results also include a focus on the overall dynamic behavior of the structure. In addition to the two 1:25 models, a 1:37 model was also tested at MARIN, utilizing the MARIN stock wind turbine. This model is also included in the comparison. Therefore the different scales are considered but the comparison is presented exclusively for wave loads as only the 1:37 model was tested under wind and wave conditions.

Analysis of Structural Vibrations of Vertical Axis Wind Turbine Blades via Hamilton’s Principle — Part 1: General Formulation

2020 ◽  
Vol 20 (09) ◽  
pp. 2050098
Author(s):  
Jianyou Huang ◽  
Chia-Ou Chang ◽  
Chien-Cheng Chang
Keyword(s):  
Imaginary Part ◽  
Coriolis Force ◽  
Wind Turbines ◽  
Natural Frequencies ◽  
Vertical Axis ◽  
Lateral Bending ◽  
Structural Vibrations ◽  
Blade Length ◽  
Axial Torsion ◽  
Axial Tension

Energy harvesting by wind turbines is of great concern in many countries/areas, yet its safety is inevitably related to the structural vibration of the turbine system. In this study, we present a complete linear analysis of structural vibrations for vertical axis wind turbines (VAWTs) based on Euler’s beam theory by Lagrangian mechanics. The un-deformed blade is assumed to be vertically straight. There are several findings from solving the resultant equations which represent four dimensions of deformation, involving motion: lateral bending-chordwise bending-axial torsion-axial extension (BBTE) (1) There is no deformation coupling between axial tension and axial torsion. (2) The natural frequencies of the blade are mainly determined by lateral bending, and [Formula: see text] ([Formula: see text]) denote the natural frequencies determined solely by lateral bending. (3) The centrifugal force credited to blade deformation is the primary factor that modifies the natural frequencies. (4) The Coriolis force can exist only in the coupled system, but in any case, the Coriolis force will not be generated by coupling lateral bending and axial tension. (5) The Coriolis force, when lateral bending is coupled with chord bending or axial torsion, can only slightly modify the natural frequencies. (6) In the case of fixed speed of rotation, [Formula: see text], where [Formula: see text] is angular speed and [Formula: see text] is the distance from the rotation axis to the elastic center of the blade: given [Formula: see text]-the blade length to chord ratio, it is found that the natural frequencies [Formula: see text] of the blade are, in close approximations, inversely proportional to [Formula: see text], i.e. [Formula: see text], where [Formula: see text] is the base chord length and [Formula: see text] is the base blade length. (7) In the general case of rotating blade ([Formula: see text], we let [Formula: see text] denote the [Formula: see text]th natural frequency when [Formula: see text]. It is found that the natural frequencies [Formula: see text] are closely approximated by [Formula: see text] (8) The material damping yields the imaginary part of the modified system frequency [Formula: see text], which deteriorates the energy absorption rate of the blade. Perturbation analysis with a solvability condition is performed to determine the imaginary part of [Formula: see text]. Given the same material, [Formula: see text] is inversely proportional to [Formula: see text], i.e. [Formula: see text].

Modal Analysis of a Drilling Machine for Blades of Wind Turbines

2011 ◽  
Vol 308-310 ◽  
pp. 1850-1854
Author(s):  
Yong Shu Jiao ◽  
Yong Liang Zhang ◽  
Mu Hui Fan
Keyword(s):  
Modal Analysis ◽  
Wind Turbines ◽  
Software Package ◽  
Natural Frequencies ◽  
Position Angle ◽  
Simplified Model ◽  
Drilling Machine ◽  
Structural Stress ◽  
Specific Working

In this paper, the authors conducted a modal analysis of a drilling machine for blades of wind turbines. A simplified model of the machine was established with a commercial FEM software package, Ansys. At a specific working position the first six order natural frequencies were calculated and the results obtained from two different contacting manners were compared. The influence of static structural stress induced by gravitational load on natural frequency was also evaluated. The variations of the natural frequencies of the machine with the position angle of the rotary box were subsequently obtained. This is helpful for the determination of range of the excitation frequencies.

The Influence of the Joint Wind-Wave Environment on Offshore Wind Turbine Support Structure Loads

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Puneet Agarwal ◽  
Lance Manuel
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Environmental Conditions ◽  
Field Data ◽  
Probabilistic Approach ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Design Loads ◽  
Wind Regimes

Our objective here is to establish long-term loads for offshore wind turbines using a probabilistic approach. This can enable one to estimate design loads for a prescribed level of return period, generally on the order of 20–50years for offshore wind turbines. In a probabilistic approach, one first needs to establish “short-term” distributions of the load random variable(s) conditional on the environment; this is achieved either by using simulation or field measurements. In the present study, we use field data from the Blyth offshore wind farm in the United Kingdom, where a 2MW wind turbine was instrumented, and environment and load data were recorded. The characteristics of the environment and, hence, that of the turbine response at the site are strikingly different for wind regimes associated with different wind directions. Here, we study the influence of such contrasting environmental (wind) regimes and associated waves on long-term design loads. The field data, available as summary statistics, are limited in the sense that not all combinations of environmental conditions likely to be experienced by the turbine over its service life are represented in the measurements. Using the available data, we show how distributions for random variables describing the environment (i.e., wind and waves) and the turbine load of interest (i.e., the mudline bending moment) can be established. By integrating load distributions, conditional on the environment with the relative likelihood of different environmental conditions, long-term (extreme/ultimate) loads associated with specified return periods can be derived. This is demonstrated here by carefully separating out the data in different wind direction sectors that reflect contrasting wind (and accompanying wave) characteristics in the ocean environment. Since the field data are limited, the derived long-term design loads have inherent uncertainty associated with them; we investigate this uncertainty in such derived loads using bootstrap techniques.

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